In recent years, the employment of a fuel cell as a power source for various kinds of mobile instruments such as a laptop computer, a cellular phone, etc. has been extensively practiced in order to enable these mobile instruments to be used for a long period of time without necessitating the charging of the power source. This fuel cell is featured in that the generation of power can be effected therein simply through the feeding of fuel and air thereto, so that it is possible to continuously generate electric power for a long period of time as long as it is replenished with only fuel. Therefore, if it is possible to miniaturize the fuel cell, it will become a very advantageous system for use as a power source for these mobile instruments.
Especially, in the case of a direct methanol fuel cell (DMFC), since methanol having a high energy density is employed as a fuel and an electric current is directly extracted from methanol by making use of a catalytic layer and a solid electrolyte film, it no longer requires the employment of a reformer, thus making it possible to miniaturize the fuel cell, and, at the same time, the handling of fuel is easier as compared with hydrogen gas, thus making it more advantageous as a power source for use in a small mobile instrument. As for the fuel supply system of DMFC, there are known various types, including a gas supply type DMFC wherein a liquid fuel is vaporized and delivered into the fuel cell by means of a blower, etc.; a liquid supply type DMFC wherein a liquid fuel is delivered as it is into the fuel cell by means of a pump, etc.; and an internal vaporization type DMFC wherein the liquid fuel delivered into the fuel cell is vaporized therein and then fed to the fuel electrode thereof.
As described in JP-A 2000-106201 (KOKAI), the internal vaporization type DMFC is provided with a fuel penetration layer for retaining liquid fuel, and with a fuel vaporization layer for diffusing a vaporized fuel component out of the liquid fuel retained in the fuel penetration layer, thereby enabling the vaporized fuel to be fed from the fuel vaporization layer to the fuel electrode. According to the above-described document, an aqueous solution of methanol consisting of a 1:1 molar mixture of methanol and water is employed as the liquid fuel, and both of methanol and water are turned into a gaseous state before they are fed to the fuel electrode. However, the fuel cell wherein an aqueous solution of methanol is employed as liquid fuel as described above is accompanied with a problem that, due to a difference in vaporization rate between methanol and water, it is difficult to derive sufficient output characteristics. Under the circumstances, in the attempts to enhance the output characteristics of the fuel cell and to further miniaturize the fuel cell, the development of the fuel cell using pure methanol as fuel is now extensively studied.
As for the small fuel cell which is mainly designed to be used in a mobile instrument, a passive fuel cell is now being developed, wherein pure methanol is employed as fuel without necessitating any active transferring means such as a fuel pump for delivering the pure methanol to the fuel electrode. In the case of this passive fuel cell, in order to facilitate the operation to feed pure methanol from a fuel cartridge to the fuel tank mounted on the fuel cell, a quick disconnecting type coupler is employed at a portion of the fuel tank which is adapted to be connected with the fuel cartridge. This quick disconnecting type coupler is constructed such that it is constituted by a couple of coupling members in each of which a valve is incorporated. Each of these valves is designed to be actuated such that, under the condition where the coupling member is disconnected from the fuel cartridge, the channel inside each of coupling members is closed and, under the condition where the coupling member is connected with the fuel cartridge, the channel inside each of coupling members is opened. In this quick disconnecting type coupler which is constructed as described above, a steel spring is generally installed in the interior of each of the coupling members in order to make it possible to open or close the valve in conformity with the connection or disconnection of the coupling member in relation to the fuel cartridge.
Incidentally, there is a problem in the case of the fuel cell where pure methanol is employed as fuel that, if the methanol is contaminated with metal ions, the metal ions are permitted to be captured by the solid electrolyte film constituting an electrode film structure, thereby resulting in the deterioration in output of the fuel cell. Especially, in the case of a small fuel cell for use in a mobile instrument, since methanol is directly fed from the fuel cartridge to the fuel tank mounted on the main body of fuel cell and the methanol in the fuel tank is then fed, as it is, to the electrode film structure without being subjected to any special pre-treatment. Therefore, it is necessary, to the greatest extent possible, to avoid the contamination of methanol with the metal ions.
However, when a quick disconnecting type coupler is used at a junction between the fuel tank and the fuel cartridge, metal ions are permitted to elute into pure methanol from a metallic member included in the components of the valve, thereby giving rise to the deterioration of the electrode film structure. Especially, aluminum ions originating from a minute amount of aluminum contained in steel is harmful.